1. Field of the Invention
The present invention relates to a connector for use with a fiber optic sensor array system. More particularly, this invention pertains to a connector for simultaneously completing a plurality of reliable low-loss optical interconnections between the upstream on-board elements (e.g. source and photodetector) and downstream elements such as an optical cable or a towed array of hydrophones.
2. Description of the Prior Art
U.S. Pat. No. 5,590,229 of Goldman et al. covering "Multichannel Fiber optic Connector" addresses problems posed, for example, by hydrophone arrays that require maintenance of multiple reliable optical contacts within the operational environment. Optical fiber connections, unlike electrical connections, require precise alignments of mating fibers and are subject to significant degradation by environmentally-related factors. The failure to obtain precise alignment of fiber terminations can contribute significantly to optical signal loss.
The device disclosed in the patent includes a two-part connector, each half accommodating a plurality of optical fibers for simultaneously completing optical-quality connections between paired fibers. One fiber is accommodated in one half of the connector and the other held in the other half. The connector provides an interface for coupling optical signals from the hydrophones of either a towed or planar array to upstream shipboard elements including, for example, a laser source, a photodetector and processing electronics. Should a grouping of seven (7) hydrophones be employed, for example, a total of fifteen (15) fiber couplings must be accomplished by the connector.
The device of the referenced patent is designed for extremely high performance applications characterized by very high return loss in operation. This results in a rather complex and difficult-to-manufacture structure that is necessarily quite costly. In the device of the patent, multiple optical fibers with ferrule terminations are spring-loaded within a plurality of internal channels of each of the connector halves. The stringent return loss requirements demand that not only axial, but also rotational, alignment be maintained between the faces of contacting fibers. As a consequence, the faces of the ferrules are angularly-inclined, necessitating a rotational alignment structure for assuring that mating angular alignments are simultaneously obtained among the plurality of pairs of fibers housed in the two connector halves.
The structures required for rotational alignment include the keyed ends of the cups into which the ferrules are inserted, in combination with the slotted rear faces of body elements of the male and female connector halves. The fabrication of each of such elements is complex and requires precision machining, reducing yield while increasing cost and complexity.
In contrast to the types of optical interconnections and associated connectors required to maintain rotational, as well as axial, alignment precision in the most demanding applications, there exist many useful applications that do not require rotational alignment between mating optical fibers for satisfactory performance. FIGS. 1(a) and 1(b) are side sectional views illustrating a ferrule 10 having a symmetrical face (as opposed to one that is angularly-inclined for rotational alignment). Such a ferrule 10 is suitable for optical interconnections in numerous, primarily non-military, applications.
The ferrule 10 comprises a generally cylindrical elongated body with an outer shell 12, preferably of tungsten carbide, that encloses a filler material 14 (preferably a relatively soft silver/nickel alloy). The filler material 14 encircles an optical fiber 16, substantially encapsulating it within a shaped fitting 18 of EPOXY or like adhesive. A brass element 20 stiffens the fiber 16. An outer plastic coating 22 is stripped from the fiber 16.
FIG. 1(b) is an enlarged and detailed view, taken at line 1(b) of FIG. 1(a), of the terminal end of the optical fiber 16 in optical contact with an optical fiber 16' (shown in shadow outline). The fibers 16 and 16' include polished termination end faces 24, 24' that are continuations of, and substantially coextensive with, faces 26 and 26' of the respective ferrules. It is to be noted that the end faces 24 and 24' and the faces 26 and 26' are symmetrically rounded about the cores of the optical fibers 16 and 16'. Thus, there exists a small region of mutual tangency between the fibers 16 and 16', facilitating the transmission of optical signals therebetween. Also, oppositely-acting axial compression forces (introduced by springs) tend to flatten the rounded end faces slightly in the region of mutual tangency. The area of intimate contact between the aligned faces is thereby slightly enlarged and stabilized to enhance the quality of the optical interconnection in a manner that is entirely satisfactory for all but the most demanding optical communication criteria.